The present disclosure relates to an image forming apparatus including a plurality of photosensitive drums along a transferring belt.
An image forming apparatus of an electrographic manner includes a plurality of photosensitive drums along a transferring belt and includes a plurality of primary transferring parts with respect to the respective plurality of photosensitive drums. A surface of each photosensitive drum is electrically charged and exposed according to image data to thereby form an electrostatic latent image, and further, a toner of each color is deposited to the electrostatic latent image and developed to thereby form a toner image of each color. The toner image of each color formed at each photosensitive drum is primarily transferred to a transferring belt by each primary transferring part to which a voltage of opposite polarity to the toner is applied, and accordingly, a toner image of full color is formed.
In order to supply a suitable transferring current to each primary transferring part, it is necessary to apply a transfer voltage according to a resistance of a transferring member, such as a roller or a belt, constituting each primary transferring part. However, the transferring member, such as the roller or belt, constituting each primary transferring part may be degraded due to temperature change or aged deterioration, and a resistance value may be varied. Therefore, it is necessary to correct the transfer voltage according to variation of the resistance value of each primary transferring part.
For example, an image forming apparatus includes: an image carrier in which a developer image is formed on its surface; an intermediate transferring body to which the developer image is transferred; and a secondary transferring means transferring the developer image from the intermediate transferring body to a recording medium by applying a secondary transferring bias to a secondary transferring part. A volume resistance rate of the intermediate transferring body has temperature dependency. The image forming apparatus also has a temperature sensing means sensing temperature of the intermediate transferring body. In addition, according to a result of temperature sensing by the temperature sensing means, impedance (resistance value) of the secondary transferring part is sensed, and then, an applied voltage of the secondary transferring bias is controlled.
However, because detection of the resistance value of the transferring member takes time, in a construction including a plurality of primary transferring parts for the respective toner colors as a color printer, further time is required to measure the resistance value of each primary transferring part. In addition, if a transfer voltage is corrected according to variation of the resistance value of each primary transferring part, a furthermore time is required. Thus, productivity of printing process utilizing the plurality of primary transferring parts may be impeded.